The present invention relates to lean direct fuel injection combustion. More particularly, the present invention relates to a fuel combustion chamber and a method of and a nozzle for mixing of liquid fuel and air in such chamber, for example in a gas turbine engine, including an aircraft engine.
Several lean direct fuel injection (LDI) concepts have recently been considered for advanced gas turbine engine development. Although some of the concepts have shown acceptable combustion results, the geometrical configuration of the fuel-air mixers is complicated, and the combustion results have not been fully satisfactory. Development of new fuel injectors to be applied to LDI concepts is of great importance in development of advanced gas turbines. For the past several years, conventional fuel injectors, such as air-blast atomizers and pressure atomizers, have been utilized in development of high-performance gas turbine engines. However, more practical fuel injectors which are less prone to clogging are needed for future advanced aircraft engines.
Objectives of this invention are to produce rapid and uniform mixing of liquid fuel and air in combustion zones and to provide high thermal performance and low emissions in aircraft gas turbine engines. Developing advanced gas turbine engines for all speed ranges--subsonic, supersonic, and hypersonic--is one of the most urgent and important areas of aeronautical research and development. Achieving high thermal efficiency and low emissions, especially, NO.sub.x, from the gas turbine engines is a major objective. As a first step to achieving this goal, increase of the inlet air compression ratio (up to 60 to 1) and fuel-lean burning have been proposed, leading to the lean direct fuel injection (LDI) concept at high pressure and temperature. In the LDI concept, combustion performance, especially emission generation, depends to a great degree upon the quality of the fuel-air mixing in the combustion zone. Problems that have been encountered include (1) providing rapid and uniform mixing of lean-fuel and rich-air in a direct injection mode, (2) improving flame stability under lean combustion conditions, (3) reducing power loss through the fuel-air mixing process, and (4) preventing clogging of injector orifices.
Since the LDI concept was introduced to aircraft engine manufacturers, some preliminary emission tests have been done by agencies of the United States government, aircraft engine companies, and academic institutions. Such tests have revealed that the LDI concept has a potential for future advanced gas turbine engines and that LDI combustion performance depends to a great degree upon the quality of fuel-air mixing.
In the LDI mode, liquid fuel is directly injected in a fuel lean ratio into a burning zone which is confined and compact. This injection method is in reality an extension of the current lean-premixed-prevaporized (LPP) concept. However, the major difference is that LPP physically separates the fuel-air mixing process from the combustion process, while LDI does not. Also, flame stabilizing is built into the fuel-air mixing process, rather than having a separate flame-holder.